The present invention relates to improvements in a control system for a continuously variable transmission (CVT) for a vehicle, and more particularly to a control system of a belt type CVT.
A Japanese Patent Provisional Publication No. 8-200461 discloses a typical belt type CVT which comprises driver and follower pulleys and a belt for intercoupling the pulleys. Each of the driver and follower pulleys has a variable groove at which the belt is held. A belt holding force for holding the belt by each pulley is varied basically according to a line pressure which is produced by pressurizing a fluid by means of a pump through a CVT pressure control valve. The line pressure is increased according to the increase of an input load applied from an engine to the CVT. The input load is basically calculated from a throttle opening and an engine revolution speed of an engine. Further, a clutch pressure for controlling a start clutch such as a forward clutch and a reverse brake disposed between the engine and the CVT is produced from a branch pressure of the line pressure and is controlled by means of a clutch pressure control valve to establish the engagement between the engine and the CVT.